The decisions in the trace that are skipped during replay are
only those that are known a priori to be unjustified.
This does not
guarantee that the skeletal plan which is left will
ultimately be refined into
a solution for the current problem.
Without actually completing
the search there is no way of predicting whether the constraints
that are left in the skeletal plan are consistent with a complete
solution.
Whenever the skeletal plan is not complete
(whenever there are extra goals or unsatisfied initial
state conditions) the planner must undergo further planning effort
to extend the plan
and there is a possibility that this
effort may fail, necessitating a recovery phase.

For DERSNLP+EBL, the skeletal plan is extended first, prior to recovery.
This plan is backtracked over only after the search process
fails to refine it into a full solution to the new problem.
This strategy requires a depth limit to be
placed on the search tree.
Otherwise skeletal plan extension may
continue indefinitely, and the planning algorithm becomes incomplete.
An eager extension strategy is not, however, linked to a particular
search method.
For example, it may be used
with best-first, depth-first or iterative deepening search. These
different search methods are used in the exploration of
the subtree under the skeletal plan, prior to
backtracking over this plan.
Once the skeletal plan is found to fail, the recovery phase
that is initiated merely involves exploring the siblings of the
replayed path. Like extension, recovery is not linked to a
particular search strategy.